1. Field of the Invention
The present invention relates to a gateway device arranged to relay transmission and reception of electronic mails (e-mails) and, in particular, relates to a processing technique for transmitting and receiving the e-mails by the gateway device.
2. Description of the Related Art
A gateway device that is arranged between a client and a server and that relays transmission and reception of e-mails is well known. Some gateway devices of this type include a function for encrypting/decrypting the e-mails.
The conventional gateway device includes a storage unit that stores the e-mails. In order to store a large number of e-mails, the storage unit preferably has a large capacity. However, as the capacity of the storage unit increases, a substantial storage with a large capacity is required, thereby affecting the production cost and management cost. Accordingly, a gateway device including a storage unit that shows good performance in spite of a small capacity and that requires only a small storage has been desired.